6.1.1 Cellular Control Flashcards
Defintion of gene mutation and the 3 types
A change in the sequnce of base pairs that may result in an altered polypeptide
Insertion, subsitition, deletion
Why may a mutation result in no change to the polypeptide
Genetic code is degenerate so serval different triplets code for the same amino acid
Lots of the interaction in polypeptides depend on wether the amino acid is hydrophobic or hydrophilic, a wrong amino acid can still have the correct effect
Insertion
A nucleotide is randomly inserted into the DNA sequence
This change has a knock on effect as every bass after the insetion is wrong (known as frameshift mutation)
This may dramatically change the amino acid sequence produces from this gene and therefore the abilty of the polypeptide to perform its function.
Deletion of nucletoides
A nucleotide is randomly deleted from the DNA sequence
Changes the amino acid that would have been coded for, also has a knock on effect as every base is 1 position forward
Frameshift mutation
Dramatically changes polypeitde
Substitution
A base in the DNA sequence is swapped for a different base, only changes 1 amino acid, no knock on effect
Silent mutation - does not change amino acid
Missense mutation - alters a single amino acid in the polypeptide chain
Nonsense mutation- creates a premature stop codon
Effects of mutation can be
Harmful
Neutral
Beneficial
Controls of gene expression ( 4 stages)
Transcriptional control
Post transcriptonal control
Translational control
Post translational control
Structure of the lac operon
Regulatory gene -promoter-operator-structrual genes ( z and y)
Repressor protein is bound to promoter and operator
When lactose is pressent it enters the ecoli and binds to the repressor causing it to release, RNA polymerase binds to operator and begins transcription
The structural genes are transcribed and the enzymes are synthesised
Enzymes transcribed by the lac operon
Lactose permease - moves into the membrane of the ecoil making it easier for lactose to enter the cell
Lactase - breaks down lactose - glucose and galactose , glucose is used by the cell
Types of gene and what they code for
Structural gene - codes for protein that has a function within a cell e.g enzymes, hormones
Regulatory genes - codes for a protein that control the expression of structural genes
Transcription factors and how they work
Protiens that bind to spefic reigons of DNA ( promoter reigons) to control the transcription of DNA
Binding can either allow or prevent transcription from taking place
Binding of transcription factors will either increase or decrease the rate of transcription of a gene
Difference between exons and introns
Exon - expressed region of DNA, codes for amino acids
Intron - intragenic reigon ( non coding sequences)
Why post transcriptional control is needed
When DNA is transcribed both exons and introns aretranscribed
The intron sections need to be removed from the pre-mRNA molecule
Exons fuse together to form mature mRNA that is ready for translation
This process is called splicing
Primary MRNA is also edited
Control at the post translational level
Involves modfiication to the protiens that have been synthesised e.g.
Addition of non protien groups such as carbohydrate chains , lipids, phosphates
Modifying amino acids and the formations of bonds such as dislufide bridges
Some polypeptides require activation by cyclic AMP
Cyclic AMP acitvates protein kinases which itself is a precursor enzyme which acitvates other proteins
What are Homeobox genes
Group of genes that all contain a homeobox, a homeobox is a section of DNA 180 base pairs long codes for a protein transcription factor that is exactly 60 amino acids long.
They attach to DNA at specific reigons and regulate the transcription of genes by turning various genes on and off
These reigons are highly conserved becuase any mutation would lead to the organism not surviving
Homeobox genes are responsible for the genetic control of the development of body plans
Hox genes
Are one group of homeobox genes only present in animals
Are a set of transcription factors that are only present in animals and are responsible for the correct positioning of body parts
Hox genes are found in gene clusters, mammals have four clusters
The order in which they appear along the chromosome is the order in which their effects are expressed on the organisms
Protein kinases
Enzymes that catalyse the additon of phosphate groups to proteins
The additon of a phosphate group changes the tertiary structure and therefore the function of the protein
Protein kinases are activated by cyclic AMP
What is apoptosis
Programmed cell death
Importance of mitosis and apoptosis
Constant replacing and destruciton of cells in early development
Some cells produced by mitosis are no longer needed therefore they are destroyed
E,g fingers and toss are developed as single combined units then are seperated later by programmed cell death
How can genes which regulate the cell cycle and apoptosis be effected
Internal cell stimuli - internal factors that affect apoptosis and cell cycle
irrepareable genetic damage, RNA decay : these factors can initiate apoptosis in cells that are undergoing cell stress
External cell stimuli - external factors that affect apoptosis and cell cycle
Presence of signaliing molecules: cytokines, hormones
Virsus and bacteria, damaging cells faster than they can be replaced
Cells often respond to such stressful stimuli by activating pathways to increase their chance of survival or initiating apoptosis
Relationship between regulatory and structural genes
Regulatory genes control the expression of structural genes
Function of DNA and RNA polymerase
DNA polymerase - involved in semi conservative DNA replication, works on 2 strands
RNA polymerase - make m/t/r RNA and involved in transcription, works on 1 strand
Why meiosis needs 2 divisions
Diploid to haploid 46 chromosomes to 23
Separate homologous pairs and then sister chromatids
Role of PCR
amplify the volume of DNA trying to be sequenced
Giving DNA sections with a range of different lengths
Role of electrophoresis
- Allows DNA sample to be spread out based on length / size
- order of bases can be read
Role of restriction enzymes
Cut DNA into fragments so it can be read
Why genome has to be fragmented before sequencing
Genome is too large to sequence as a whole
Sequencing is more accurate when cut
How has the knowledge of apoptosis helped science
Allows us to understand and treat tumours and autoimmune disease
Where does RNA polymerase bind on the lac operon
Promoter region
